An oak forest and three wet meadows/fens were reinvestigated after 50 years concerning tree vitality, biomass and productivity, and soil chemistry. Sulphur and nitrogen deposition has changed dramatically during these years, and the aim was to analyse the differences in both the oak forest and the open field ecosystems. Trees were re-measured and soil profiles were resampled. Important visible changes in the oak forest were stated concerning the vitality of oaks. Aboveground there was a decrease in tree biomass, production and litter fall, but a huge increase in standing dead logs. During the years, the deposition of sulphur had decreased drastically, but nitrogen deposition was still high. Soil acidification in the forest had decreased, reflected in an increased base saturation in the forest, in spite of slightly lowered pH-values. Strongly increased amounts of exchangeable Ca and Mg now appeared in the forest soil, and a substantial transport of calcium and magnesium had obviously taken place from the forest soil to the meadow and fens during the years. However, the most important soil change was the accumulation of organic matter. The increased accumulation of organic matter in turn meant increased amounts of colloid particles and microsites for ion exchange in the soil. This favoured 2-valence base cations, and especially Ca and Mg that increased very much in all the studied ecosystems. Carbon as well as nitrogen had strongly increased in the forest, meadow and fen soils. This was interpreted as a natural result of increased vegetation growth due to high nitrogen deposition, increased global annual temperature and increased carbon dioxide concentration in air. It was concluded that the decreased deposition of sulphur had had a positive effect on soil chemistry, and that the deposition of nitrogen probably had stimulated vegetation growth in general, and contributed to increased amount of organic matter in the soils. However, in this studied oak forest, the decreased vitality and many killed trees were also suspected to be a result of high nitrogen deposition. Obviously increased tree growth was counteracted by decreased stress resistance, and increased appearance of pathogens in the oak trees.
The area Linnebjer was subject to an investigation of soil and vegetation already at the end of the 1950s. It was intensively followed until the 1970s. The results were synthesised in a doctoral thesis [
As a background to the present paper the major results of the first investigations will be summarised. Linnebjer is a nature reserve seven km ENE of Lund, S Sweden of 38 ha, dominated by a pedunculate oak, lime and hazel forest intermingled with small, moist areas, mostly with meadow and fen vegetation. The forest should be seen as remnants of a forest, which earlier was subject to a different utilisation and management than today. The bedrock consists of Silurian slate covered by a shallow layer of clay mixed with rests from the calcareous bedrock area a few km further south. A Special area of 130 × 140 m was intensively investigated in the northern part. Plants, vegetation, soil water conditions as well as soil chemical and physical properties were mapped and classified [
The identified ecosystems appear in a gradient from dry, or more properly moderately fresh, to wet conditions. The soil and terrain regulate the governing factor, the ground water, in a way that the forest has a good aeration, while the meadow and fen ecosystems have less good oxygen conditions. In the forest there is a dominating vertical water movement, while in the meadow ecosystems mainly a lateral water movement prevails. The forest is dominated by an Oxalis acetosella-ecosystem. The meadows are dominated by a Filipendula ulmaria-ecosystem and more fen-like ecosystems with Carex caespitosa and Carex flacca, respectively.
The discussed vertical and horizontal water movements result in forest soils with rather acid mull, and meadows/fens with humus types of more or less neutral reaction. A gradient of humus types from mull to fen-mull and anmoor were found. The humus types have different chemical properties as a result of the mediating effects of the water factor. The most expressive evidence of this circumstance is seen in the distribution of pH and the percentage of exchangeable metallic cations. A number of other soil chemical factors vary along these gradients, e.g. nitrogen mineralisation, turnover of phosphorus and potassium.
As stated above the Linnebjer forest is a nature reserve and a remnant of an earlier large forest―the “Skrylle forest”. Today one can locally find small patches of this forest still remaining in the area. Linnebjer is such an example. The development of these forests depended on Man’s use of the forests―in other words the impact of Man was and still is important for their development.
The historical development and the use of the present Linnebjer reservation is discussed by [
In later time the Linnebjer forest become dominated by oak, linden and hazel. Oaks had a timber value, often belonging to the State. Linden produced long and slender poles for roof building. Hazel was used as reinforcing rods in building “clay houses”, typical for the landscape. The vegetation is described in [
Originally the Linnebjer forest was owned by the State―The Swedish Forest Service. It was early set aside as a nature reserve due to its characteristics. In 1980 the area was bought by the National Trust of Sweden administrated by the Swedish Nature Conservancy Board. Simultaneously the Local County Board became responsible for the maintenance. Today the Linnebjer nature reserve is enlarged and includes also areas north of the reserve with open fields and a magnificent view of an open landscape. It is designated as an area belonging to Natura 2000 in order to promote habitats for plants and animals (
Linnebjer has a preservation plan dated 2005-12-16 (Plan for maintenance 2005―In Swedish: Bevarandeplan, Linnebjer). From now on there is a national interest connected to the area as to vegetation and species. The dominating area is covered by a Quercus robur, Tilia cordata and Corylus avellana forest (22.5 ha), Fagus sylvatica forest (1.4 and 0.1 ha, rich in herbs and Luzula pilosa, respectively), a meadow with tall herbs (0.9 ha) and dry-fresh species representing rich lowland grassland of Fennoscandia type (4.3 ha). The latter is situated north of the Special area (
Half a century is a long time. Some changes have been observed with the naked eye and not documented, others have been documented. Recent observations indicate that there is in general a dynamics in vegetation, which is greater than before. Today there are more wind throws, more dying or dead trees as well as a more intensive management of the meadows, especially in the Special area.
The aims of this paper are:
- To describe the increased vegetation changes and its causes.
- To analyse the possible effects of the increased/decreased deposition of sulphur and nitrogen with respect to soil acidification and effects on nutrient availability on plant growth.
- To analyse the present tree biomass and productivity.
- To analyse changes in carbon, nitrogen and nutrients in the soil.
The methods applied for the studies of trees follow [
Soil sampling was performed at three of the earlier studied sites. Similar sampling procedure and soil treatment was used as is described in [
No specific investigations have been made for analysing the forest ground vegetation changes. The forest tree vegetation has been considered to be in a kind of “steady state”. During the last 20 years it was, however, obvious that especially mature oaks were hit by “oak disease”. The vitality of many trees decreased, and many trees appear today as half-dead or dead [
The dieback was apparent in a specific study of the tree biomass and production of the forest (
The latest intervention by Man was the establishment of paths in the forest, which required that some oak trees were taken away. Further, the opening of the meadow of the Special area also required felling of some trees.
The observed changes in the tree layer raised a question if the tree biomass and production had changed. By assuming that the allometric regressions for these properties of the forest still were valid a comparison between values from 1967 and 2015 could be done. A revision of the earlier measured areas [
Deposition of air pollutants as sulphur and nitrogen were measured in Linnebjer 1966 and 1967 in the open field and in the oak forest. Very high values of sulphur in forest throughfall were measured, 34 kg∙ha−1. 22 kg∙ha−1 of nitrogen was measured in the forest as well. Unfortunately no on-site measurements are available today (
Healthy | Half healthy | Dead | Stumps | Total | |
---|---|---|---|---|---|
Block I | 9 | 2 | 2 | 5 | 18 |
Block II | 7 | 0 | 7 | 0 | 14 |
Block III | 7 | 2 | 2 | 0 | 11 |
Sum 0.48 ha | 23 | 4 | 11 | 5 | 43 |
Trees ha−1 | 48 | 8 | 23 | 10 | 89 |
Species | Above-ground biomass | ||||||
---|---|---|---|---|---|---|---|
Sample area no and area in ha | Total 0.48 | Total/ha | |||||
I (0.16 ha) | II (0.16 ha) | III (0.16 ha) | Ton | Ton∙ha−1 | |||
Quercus robur | 27.0/22.3 | 30.2/15.0 | 17.4/21.0 | 74.6/58.3 | 155.3/121.5 | ||
Corylus avellana | 3.0/1.3 | 2.4/2.1 | 2.0/1.17 | 8.4/4.9 | 17.4/10.1 | ||
Other species | 2.1/0.3 | 3.1/0.3 | 8.5/10.6 | 137/10.1 | 28.5/23.2 | ||
Total above ground | 32.1/23.8 | 36.7/17.7 | 27.9/32.8 | 96.7/73.3 | 201.2/154.8 | ||
Dead trees (oak) | -/4.12 | -/11.03 | -/4.45 | -/19.6 | -/40.8 | ||
Species | Above-ground yearly production | ||||||
Sample area no and area in ha | Total 0.48 | Total/ha | |||||
I (0.16 ha) | II (0.16 ha) | III (0.16 ha) | Ton | Ton∙ha−1 | |||
Quercus robur | 1.06/0.84 | 1.25/056 | 0.69/0.76 | 3.00/2.16 | 6.25/4.50 | ||
Corylus avellana | 0.45/0.22 | 0.64/0.39 | 0.36/0.18 | 1.45/0.80 | 3.02/1.64 | ||
Other species | 0.19/0.05 | 0.27/0.03 | 0.54/0.63 | 1.00/0.71 | 2.08/1.48 | ||
Total above ground | 1.70/1.11 | 2.16/1.00 | 1.59/1.57 | 5.45/3.66 | 11.35/7.63 | ||
Dead trees (oak) | -/0.17 | -/0.44 | -/0.14 | -/0.75 | -/160 | ||
Ecosystem | Time | SO4-S | Ntot | Reference | |
---|---|---|---|---|---|
Linnebjer, S | Open field | 1967 | 11.0 | 9.3 | [ |
Quercus | 1967 | 34.4 | 22.4 | ||
Quercus | 2013 | 4 - 6 | 12.0 | ||
Baldringe, S | Fagus | 2013 | 3 | 9 | [ |
Skovbjer, DK | Open field | 1997-2000 | 7.8 | 12.9 | [ |
Quercus/Fagus | 1977-2000 | 11.5 | 20.2 |
A comparison with other measurements must be done. Values from Baldringe, not so far from Linnebjer, indicate a substantial decrease of sulphur. For nitrogen it is more difficult. A high open field value is assumed, but the throughfall is unsure. The Danish values can be used as a support.
Total carbon (C) and nitrogen (N) of the soil profiles and the estimated C/N-ratios are given in
Vertical flow 1966/2013 | |||||||||
---|---|---|---|---|---|---|---|---|---|
Ecosystem and depth | pH | pH | Base sat. | Na | K | Ca | Mg | Mn | H |
H2O | KCl | % | mmol dm−3 | mmol dm−3 | mmol dm−3 | mmol dm−3 | mmol dm−3 | mmol dm−3 | |
Oxalis acetosella forest | |||||||||
0 - 10 cm | 4.6/4.2 | 3.5/34 | 17/20 | 0.88/0.71 | 2.08/1.66 | 4.8/13.5 | 2.1/6.8 | 0.32/0.83 | 86/86 |
10 - 20 cm | 4.3/4.3 | 3.5/3.4 | 11/22 | 0.97/1.11 | 1.44/0.69 | 2.8/12.8 | 2.1/11.2 | 0.07/0.22 | 93/86 |
20 - 30 cm | 4.7/4.6 | 3.7/3.6 | 11/28 | 1.18/1.01 | 1.47/0.57 | 2.8/13.3 | 2.5/11.9 | 0.05/0.10 | 105/67 |
30 - 40 cm | 4.4/4.8 | 3.4/3.7 | 13/32 | 1.85/1.03 | 2.04/0.55 | 2.9/14.5 | 3.2/14.3 | 0.05/0.05 | 107/49 |
Horizontal flow 1966/2013 | |||||||||
Filipendula meadow | |||||||||
0 - 10 cm | 6.5/6.3 | 6.1/5.5 | 90/90 | 1.07/0.58 | 2.48/1.49 | 37/213 | 11/74 | 0.01/0.53 | 22/30 |
10 - 20 cm | 6.3/6.5 | 5.6/5.6 | 87/91 | 2.15/1.00 | 3.73/1.37 | 59/172 | 19/66 | 0.01/0.12 | 27/23 |
20 - 30 cm | 7.0/6.8 | 6.4/5.3 | 87/89 | 2.74/1.52 | 4.12/3.33 | 66/190 | 26/85 | 0.03/0.05 | 28/36 |
Carex flacca fen | |||||||||
0 - 10 cm | 7.1/6.2 | 6.4/5.6 | 92/90 | 1.21/4.46 | 0.79/1.84 | 36/248 | 10/80 | 0.03/0.04 | 7/36 |
10 - 20 cm | 7.3/6.1 | 6.2/5.0 | 92/87 | 2.11/5.48 | 0.74/1.14 | 13 | 18/56 | 0.02/0.02 | 23/31 |
20 - 30 cm | 7.0/6.8 | 6.4/5.4 | 92/90 | 3/7.18 | 0.99/1.01 | 58/132 | 20/61 | 0.01/0.00 | 20/22 |
Carex caespitosa fen | |||||||||
0 - 10 cm | 6.0/6.6 | 5.5/5.9 | 88/91 | 1.02/1.24 | 0.54/1.76 | 29/270 | 8/106 | 0.01/0.00 | 14/28 |
10 - 20 cm | 7.3/6.4 | 6.2/5.5 | 82/90 | 1.84/2.08 | 0.43/0.89 | 45/151 | 16/70 | 0.03/0.00 | 27/26 |
20 - 30 cm | 6.7/7.0 | 5.8/5.8 | 89/93 | 2.67/2.12 | 0.68/0.82 | 56/143 | 24/79 | 0.04/0.00 | 30/16 |
Ecosystem and depth | C-tot. | N-tot. | C/N |
---|---|---|---|
1966/2013 | 1966/2013 | 1966/2013 | |
g∙dm−3 | g∙dm−3 | ||
Oxalis acetosella forest | |||
0 - 10 cm | 35/56 | 3.4/5.3 | 10.3/10.7 |
10 - 20 cm | 30/40 | 2.9/4.1 | 10.5/9.9 |
20 - 30 cm | 16/27 | 2.0/2.9 | 8.0/9.3 |
30 - 40 cm | 10/17 | 1.6/2.0 | 7.5/8.5 |
ton∙ha−1 | 92/140 | 9.9/14.2 | 9.3/9.9 |
Increase (%) | 52 | 43 | |
Filipendula ulmaria | |||
0 - 10 cm | 40/106 | 2.6/10.1 | 11.6/10.6 |
10 - 20 cm | 46/78 | 3.9/8.0 | 11.8/9.8 |
20 - 30 cm | 25/54 | 4.6/6.5 | 5.4/8.3 |
ton∙ha−1 | 111/238 | 11.1/24.5 | 10.0/9.7 |
Increase (%) | 114 | 121 | |
Carex flacca fen | |||
0 - 10 cm | 44/138 | 4.3/13.0 | 10.2/10.7 |
10 - 20 cm | 52/72 | 5.2/7.8 | 10.0/9.2 |
20 - 30 cm | 32/39 | 3.5/4.7 | 9.1/8.3 |
ton∙ha−1 | 128/249 | 13.0/25.5 | 9.8/9.8 |
Increase (%) | 95 | 96 | |
Carex caespitosa fen | |||
0 - 10 cm | 50/162 | 4.5/14.5 | 11.1/11.2 |
10 - 20 cm | 67/90 | 6.5/8.8 | 10.3/10.3 |
20 - 30 cm | 49/49 | 6.4/5.7 | 7.7/8.6 |
ton∙ha−1 | 166/301 | 17.4/29.0 | 9.5/10.4 |
Increase (%) | 81 | 67 |
The total amount of C down to 40 cm in the Oxalis acetosella forest was 1966 estimated to 92 ton/ha−1, but 2013 it had increased to 140 ton∙ha−1. Down to 30 cm depth the Filipendula meadow increased from 111 to 238 ton∙ha−1, the Carex flacca fen from 128 to 249 ton∙ha−1 and the Carex caespitosa fen from 166 to 301 ton∙ha−1 (
Concerning (N) the mean content in 0 - 10 cm of the Oxalis-forest was 3.4 g∙dm−3 in 1966, and had increased to 5.3 g∙dm−3 in 2013. In the Filipendula ulmaria meadow the mean content earlier was 2.6 g∙dm−3 and increased to 10.1 g∙dm−3, in the Carex flacca fen the increase was from 4.3 g∙dm−3 to 13.0 g∙dm−3, and in the Carex caespitosa fen the increase was from 4.5 to 14.5 g∙dm−3 in the upper 10 cm. In the whole profile down to 40 or 30 cm there were similar increases to be found (
The C/N ratio is of importance in understanding tendencies of a relative accumulation of organic matter (= increased ratio), or increased decomposition including accumulation of N (=decreased ratio). In the Oxalis acetosella forest the ratio showed only a slightly increasing change from 10.3 to 10.7 in the top soil layer, and in the whole profile there was similarly a slight increase of the ratio from 9.3 to 9.9. In the Filipendula ulmaria meadow there was instead a tendency to a decrease in the upper 20 cm, but as in the two Carex fens the ratios could be regarded principally unchanged, in spite of the very strong accumulation of both C and N.
The most evident and visible change in the forest is a decrease in the vitality of the oaks. They were hit by “oak disease” during the 1990s [
In the soils, it seems obvious that a decrease in the deposition of sulphur (primarily sulphuric acid) has resulted in a change of soil acidification [
As mentioned above, the continued deposition of nitrogen is very important, as N is usually the limiting element for plant growth. Only minor reductions in SW Sweden are noticed since the 1960s, but there has been a peak during the 1980s. As observed in most areas, the leaching of nitrate from soils is very small, which means that most deposited N is accumulated in the forests [
Increased amounts of C and N in the forest soil and principally a doubling of the C and N amounts in the wet areas are of interest from many points of view. Both in the forest and especially in the meadow and the wet fens there was a strong accumulation of organic matter, with C and N increasing almost similarly (52% - 114% and 43% - 121%, respectively), though with a tendency towards slightly more C than N in most ecosystems, except in the Filipendula meadow that had a stronger N accumulation in the upper soil layers. As mentioned above the deposition of N during the last 50 years has varied, but is today relatively similar to the situation in 1960s. The amount in open field at that time was 10 - 12 kg∙ha∙yr−1, and similar amount is measured today. However, there were higher amounts during the 1970s and up to 1990 [
High N deposition, increased CO2-concentration and the accompanying temperature increase have caused a much longer vegetation period. Since 1960s the vegetation period has increased by almost 2 weeks in Southern Sweden [
Increased amount of organic matter naturally causes a decrease of pH in both water and KCl-extracts. This is seen in the forest, and even more in the open field sites. However, at 30 - 40 cm in the forest there was an opposite trend. The explanation for this might be the strongly reduced deposition of sulphuric acid, as this earlier had a strong impact also on deeper soil layers [
Finally should be added that the increased accumulation of organic matter is also of interest from a climate change point of view. It seems obvious that especially wet areas have a great capacity to accumulate C, and thus to some extent to counteract an increasing CO2-level. This is opposite to the normal findings that climate change will increase decomposition and have appositive feedback on CO2 and global warming.
Several people have during this 50 years period been involved in the investigations. During the recent reanalyses I, the principle author, have been assisted by my friend and colleague Prof. em. Bengt Nihlgård. Anders Jonshagen has assisted us at soil sampling and tree measurements in the field. In the laboratory Kurt Olsson, Maj-Lis Gernersson and Sofia Mebrahtu Wisén have done the analyses. Maj-Lis also did some analyses almost 40 years ago. Bengt has been in charge of the analyses. He is also co-author to this paper. I thank him for a never failing support over all the years.
Financial support has been received from C F Lundström Foundation, Stockholm with 110,000 SEK, used for field work and chemical analyses. Further the Extensus foundation, Uppsala has supported the field and laboratory analyses of tree biomass and growth in Linnebjer and Hestehave, Denmark with 32,950 SEK.
I also acknowledge the support from my wife Pirjo with computer technics in finalising the manuscript. The same holds for her constant encouragement.
Folke O.Andersson,BengtNihlgård, (2016) Linnebjer—A South Swedish Oak Forest and Meadow Area—Revisited after Half a Century. Open Journal of Ecology,06,74-83. doi: 10.4236/oje.2016.62008